Signaling method and apparatus



INVENTOYR I BY Ana Q A. G. COOLEY Filed May 12, 1939 SIGNALING METHODAND APPARATUS Aug. 27, 1940.

Aug. 27, 1940. G LE 2,212,808

SIGNALING METHOD AND APPARATUS Filed May 12, 1939 3 Sheets-Sheet 2INVENTOR ATTORNEY SIGNALING METHOD AND APPARATUS Filed May 12, 1959 I 3Sheets-Sheet 5 PICTURE RECORDER APPARATUS 42 45 17 a? if 1 W I? 4/ l,

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ATTOR Patented Aug. 27, 1940 Limit 2,212,808 sromrlme METHOD APPARATUSAustin G. Cooley, Hudson View Gardens, N. Y assignorto Wide WorldPhotos, Inc, New York, N. Y., a corporation of New York Application May12, 1939, Serial No. 273,162

creams. (oi. ire-e6) 1 A principal object of the invention is to providea system for producing asignaling wave wherein alternate complete cyclesare modulated in opposite directions and while the invention finds itsimmediate usefulness in the field of telefacsimile transmission,incertain of its phases it can be applied to wave signaling systemsgenerally.

Another principal object of the invention is to provide a system forproducing a signaling wave of a constant frequency wherein alternatecomplete cycles are modulated in accordance with different signals to betransmitted.

Another object is to provide a system for transmitting signals betweentransmitting and receiv-- ing apparatus requiring synchronization, andwherein a single signaling frequency is used to transmit the messagesand to derive level control signals at the receiver. When facsimilesignals are to be transmitte over a connecting link which is subject tofading, particularly where the link includes a radio channel, it isusually necessary to employ some form of automatic level control at thereceiver. In many cases radio carrier-frequency level control or A.V.,C. at the receiver is not sufiicient and it becomes necessarytherefore to transmit over a pilot channel a separate level controlsignal. However, I have found that such pilot signals do not always varyin the same direction and positions as the accompanying facsimilesignals. Patents No. 1,737,503 and No. 2154,65? disclose a .method oflevel ,control wherein a separate pilot frequency closely adjacent thefacsimile signal frequency is employed. While it is possible to achievelevel correction with the arrangement of said patents, the utmost inaccuracy is not often attainable because it is not practical to-employ apilot frequency extremely close to the facsimile signal frequency. Inaccordance with the present invention, the pilot signal and facsimilesignal are transmitted at substantially the same frequency, consequentlyany fading -'or phase discrimination alfects both alike.

Another object of the invention is to provide a method of generating awave of uniform frequency in which alternate complete cycles representfacsimile signals and intervening alternate complete cycles representpilot or level control signals. As a result, it is possible to produceat the receiving end of the system a level con- While the invention willbe described herein variations in level of the transmission link-ormedium.

A feature of the invention relates to a novel modulating'system wherebya carrier wave of uniform frequency has alternate, complete cyclesmodulated by one signal and the intervening alternate complete cyclesmodulated by a different signal. I

Another'feature relates to a novel modulating system for facsimiletransmissionwhereby a signaling wave of uniform frequency has successivecycles. modulated in opposite directions.

;trol or A. V. 0. signal which truly represents the Another. featurerelatestoa novel form of 'receiving system for use in connection with aretiongarrangement and'inter'c-onnection of parts whereby the efiects offading, phasediscrimina- .tion and'the like are substantially reduced.

'. Other features and advantages not specifically enumerated willbejapparent after a consideration of the following detailed descriptionsand the: appended claims. v

as I applied to a facsimile system, it will be under-v stood that. theinvention is not limited thereto. Likewise, while the description refersto a system of transmitting a level control signal, this phase of theinvention'can be used in any situation where two separate messages areto be transmitted on the same signaling frequency. LiketoFig. l toexplain certain conditions of operation of the invention.

Fig. 2 is a schematic circuit diagram of one form of modulating systemembodying the inarrangement according to the invention.

Fig. '7 is a modification of Fig. 6.

Referring to Figs. 1 to 1 inclusive, a description will be given oftypical modulating conditions used when the invention is applied to anelectrooptical system such as a facsimile transmission system or thelike. Fig. 1 shows a normal signal of uniform amplitude and frequency,such as an audio-frequency carrier and for purposes of explanation, inFigs. 1, 1 1 and 1, the dot-dash line represents the normal uniformamplitude throughout the figures. It will be assumed that theelectrooptical system is arranged so that a white area of the subjectmatter being transmitted, is represented by a strong signal.

sented by the dotted lines are negatively modulated. Under the samearrangement, a grey or medium tone area will be represented by the curveof Fig. 1 and a black area will be represented by the curve of Fig. 1.It will be understood of course, that the electrooptical circuits may bearranged or poled so that the curve of Fig. 1 represents a black area,in which case the curve of Fig. 1 will represent a white area. In eithercase, the picture signal for a given shade modulates successive completecycles in opposite senses or directions. Whether the signal representswhite, grey or black, the general average for any shade is constant; Theaverage re- -ceived signal level for any shade or tone value shouldtherefore likewise be constant. If any change occursin the transmissionefiiciency or level of the connecting link e. g. a radio or wire link,then as described hereinafter, the level at the receving end can bemaintained constant by suitable A. V. C. control. In any event, whatevertype of A. V. C. control is used at the receiver, it will be operatingon the same frequency as the signals to be recorded, and will on anaverage be substantially free from selective fading or phase shift. Whenthe transmission is by radio, the freedom from selective fading can befurther improved by wobbling the radio carrier a small amount infrequency and at a high rate. The side bands also may be wobbled infrequency slightly.

Referring to' Fig. 2, there is shown a typical modulating arrangementfor achieving the ob- 'jects of the invention. In this figure, only themore important parts of a facsimile transmitter are shown, it beingunderstood that any wellknown form of facsimile scanning equipment andassociated apparatus may be used. As is wellknown, the picture i orother representation to be transmitted, is mounted on the drum 2 whichis rotated around its axis and. advanced longitudinally by a suitablelead screw 3 on the drum shaft 4. Associated with the drum is anywellknown form of photo-electric translator comprising for example alight source 5, an apertured plate 6, and a lens system 1, forilluminating the picture i with a scanning light spot of elemental area.The light reflected from each successive scanned area is picked up bythe photocell 8 in the known manner. Associated with drum 2 so as to runin geared relation'therewith control grid of amplifier 2!.

--by motor 9 and gears 9 is a rotary inductor comprisinga rotaryarmature 9 having a plurality of poles or teeth l whose number isdetermined by the desired picture signal frequency to be used. Forexample, if the picture signal frequency is to be 1800 cycles persecond, the rotor 9 may be provided with 60 teeth and it may be rotatedat the rate of 1800 R. P. M. Mounted in slightly spaced relation torotor 9 is a stator l I carrying a winding l2 whereby there isintroduced into said winding impulses having a frequency of 1800 cyclesper second. Preferably winding I2, is connected to the primary windingl3 of a coupling transformerthrough an energizing battery [4 of suitablepotential. The transformer secondary I5 is preferably shunted by acondenser it for tuning out undesired harmonics and shaping the signalto a substantially sinusoidal form. The secondary l5 feeds into anetwork of the Wheatstone bridge type of which two of the ratio arms areconstituted by the resistors H and E8, and the other two ratio arms areconstituted respectively by the photocell 8 and condenser Hi. Theunbalanced bridge current fiows through a resistor 20 which ispreferably a high resistance 6. g. of the order of a megohm. The voltagedrops across resistor 20 are applied to the control grid or inputcircuit of a suitable amplifier 2i of any well-known type, the controlgrid of which is preferably biassed negatively in the usual way by abiassingbattery 22 which has also connected in circuit therewith awinding 23 through an automatic reversing switch arrangement 24, so asto reverse the phase of the current from winding 23 for each alternatecomplete cycle of the current impressed on winding l5. Thus theswitching mechanism 2 may be coupled by a suitable shaft and gearingarrangement 25 to the shaft of rotor 9. It will be understood of course,that any other well-known method of reversing the phase of the currentsin winding 23 with respect to winding l5 may be employed.

In the absence of the winding 23, if the bridge were completelybalanced, there would be no signal on the control grid of amplifier 2!.However, winding 23 when in circuit, provides for the flow at all timesof some signal current to the amplifier even when the bridge isbalanced. This minimum current may be used to regulate the average levelof the signal from the output of the amplifier.

signals result from unbalance of the bridge, the

modulation of the 1800 cycle signal applied to the amplifier 2! will bepositive. That is, the light falling on cell 8 will effectively producea signal in phase with the signal from winding 23 and cause a strongsignal to be applied to the On the other hand, if the picture signals asrepresented by the voltage drops across resistance 20 are out of phasewith the impulses from winding 23, each complete cycle of the 1800 cyclecurrent applied to amplifier 2| will be negatively modulated. That is, asignal resulting from light applied to the photo-electric cell will beout of phase with the signal from winding 23 and the net result will bea decrease in signal rather than an increase in signal. Consequently,the 1800 cycle signal in the output of amplifier 2| will have alternateI complete cycles modulated in opposite directions as explained above inconnection with Fig. 1

for example. I

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mission link 21. ,the link 21 includes a radio channel and more of .thefact that the modulation direction varies for each complete cycle of the1800- cycle signal,

the average for any shade value at the transmitter remains constant, andthe A. V. C. signal at the receiver is less likely to be affected byselective fading, phase shift or the like in the trans- This isparticularly true where especially where the radio channel is subjectedto selective fading as regards frequency.

Referring to Fig. 3, there is shown a preferred modification of thearrangement of Fig. 2. The

arrangement is substantially similar to that of Fig. 2 and correspondingparts are designated by the same numerals. lnthis arrangement, the phasecontrol winding 23 forms part of a separate transformer 28 having twoprimary windings 29, 39, each supplied by an associated inductor stator31, 32, which stators are associated with the toothed rotor 9 in such away that one winding, for example the winding 29, will produce impulsesin winding 23 in phase with complete alternate cycles of picture signalsacross resistor 28, while the other winding 39 will produce impulses 180degrees out of phase with the intervening complete alternate cycles ofthe picture signals across resistance 29. To accomplish the above, therotor Q will be similar to that of Fig. 2, but will have each alternatetooth H3 removed, so that it has 30 teeth and revolves at the rate of1800 R. P. M. The stators 3i and 32 are mounted to produce the necessaryphase relation between the respective currents induced therein andpreferably one or both of the stators is adjustable circumferentiallyaroundrotor 9 indicated by the arrows. The transformer which feeds thesignals to the bridge arrangement comprises the secondary lb and twoprimary windings 34. Winding 33 is connected through an adjustablebattery to stator winding 3i and winding 34 is connected through anadjustable battery 35 to winding 32. The winding 29 of transformer 28islikewise connected to winding 32 preferably in series with a variableresistor 3'5; and likewise winding 39 is connected to winding 3! inseries with a variable resistor 38. The winding 3! will thereforeproduce in the winding !5 of the transformer a complete cycle each timea tooth of rotor 9 passes stator 3i and these complete cycles willbespaced as represented in Fig. 4. Likewise, the stator will cause to beimpressed upon the winding 85 spaced complete cycles as shown in Fig. 4alternating with the complete cycles of Fig. LL-rue two signals combinedin the winding It will have the resultant as shown in Fig. 4 Thebalancing and unbalancing of the bridge network by the photo-cell 8 willbe the same as thatdescribed in connection with Fig. 2. However, thewinding 23 will receive signals from both stators 3i and 32 so that eachalternate complete cycle in winding 23 is out of phase with thecorresponding alternate complete cycle across resistor 2%. Consequently,as described above in connection with Fig. 2, one cycle of impulsesimpressed on winding 23 will result in a positive modulation or increaseof amplitude of the corresponding complete cycle applied to amplifier Z!and thesucceeding cycle of impulses impressed on winding across resistor23.

.ing amplifier.

. 4! of a rotary inductor.

23 will result in a negative modulation or decrease in amplitude of thecorresponding cycles and the positive modulated cycles. The reverselyThe purpose of the variable resistors 3T, 38, is to provide the properamplitude relation between the negative modulated cycles modulated-wavesare transmitted to the receiving station 28 over any suitable channel27. If the channel 2! is a radio or carrier channel, the receivingequipment 26 will include a detector for detaching the 1800 cycle signalwave and will be provided with an amplifying system having anywell-known form of A. V. C. control, the A. V-C. signal being derivedfrom the level of the received 1800 signal.

In accordance with a modification of the. invention, each alternatecomplete cycle instead of representing a picture signal may be used as alevel control signal in which event the stator .32

instead of feeding a transformer winding 3!! will feed directly into theamplifier '2! so that alternate complete cycles will be of a uniformamplitude. ture will be represented by alternate complete cyclesof 180i)cycle current modulated in accordance with. the picture and theintervening alternate cycles will be of uniform amplitude. At thereceiving station, the picture will then be printed or reproduced in anywell-known manner under control ofthe complete alternate picture cyclesand the intervening complete cycles of' otherwise steady amplitude canbe used to provide a suitable A. V. C. signal for the recordform ofdistributor maybe employed to segregate the picture cycles into thepicturerecording circuit and the A. V. C. cycles into the A. V. C.circuit for the picture recording amplifier as is wellknown in the art.If, desired however, the recording amplifier can be operated by boththe.

picture cycles and the steady cycles. Where however, the picture is tobe recorded only by the spaced picture cycles such as shown in Fig. l,

it is necessary to separate the modulated picture cycles from the steadylevel-control cycles. L

Any well-known form of distributor may be em" ployed for this purposewhich distributor will be synchronized in any well-known way with arotor 9. If desired, the receivedlllull cycle wave itself may beutilized to synchronize the distributor at the receiver with the rotor53. One typical form of distributing arrangement that may be'used isschematically illustrated in Fig.

5. The 1800 cycle signal after detection and amplification in theapparatus 39 is impressed on a stator winding it which energizes therotor The shaft ll carrying rotor A l is brought up to speed by aseparate motor (not shown) and synchronism may be main tained by anothermotor ,as described for example in application Serial No. 261,134, filedMarch 11, 1939. The stator ill preferably surrounds the rotorhubas shownso as to ener-' gize the rotor teeth uniformly. Rotor at is providedwith a series of teeth 42 corresponding to the teeth on rotor 9' at thetransmitter.

. Mounted adjacentthe rotor teeth are two second the pole l lcorresponding for example to the curves of Figs. i and 4 The rotor M isphased in any well known manner with the rotor so In that case, anywell-known In this embodiment therefore, the pict3 and the next completecycle isinduced into 7 that the pole 43 is energized in synchronism withthe pole 3i and consequently the modulated picture signals are thereforeapplied to the picture recording mechanism 55. On the other hand, thepole M feeds a signal which was transmitted as a constant amplitudesignal into the amplifier-rectifier 35 which may be used to generate abiassing signal for controlling the amplification of the amplifyingsystem in mechanism 15 in any well-known manner. So long as thetransmission efiiciency of the connecting link 2'! does not vary, theoutput of device to is uniform and the A. V. C. signal is likewiseuniform. Should the transmission level vary, the A. V. 0. signallikewise varies, correspondingly varying the amplification of therecorder amplifier. One conventional method is to have the A. V. C.signal from coil i l amplified, rectified and the rectified current isapplied to control the bias on one or more stages of the amplifier ofdevice 35.

If the system at the transmitter produces alternate complete cyclespositively modulated according to the picture areas and interveningcomplete cycles also modulated according to picture areas as describedin connection with Figs. 2 and 3, a distributor arrangement such asshown in Fig. 6, may be used at the receiver. The rotor a! may be thesame as rotor ll of Fig. which is energized under control of thereceived 1800 cycle picture signals as described, rotor 4%! beingbrought up to speed by a separate motor M as described in saidapplication Serial No. 261,184. Associated with rotor 4! are two pick-upstators 33, M, similar to the corresponding pick-up coils of Fig. 5.Connected across coil 43 is the primary winding 58 of a transformer, andconnected across coil A l is the primary winding 5! of the sametransformer. The transformer secondary 52 feeds the combined signal intoan amplifier-rectifier 53. The output of device 53 applies an A. V. C.control grid-bias potential to the amplifier 54, and also to amplifier55. Amplifier 54 feeds a picture recorder 54 which reproduces thepicture as a photo-- graphic negative from which positive prints can besubsequently made The amplifier 55 feeds a picture recorder 55 which ispreferably'of the type which reproduces the picture directly as a,positive so as to act as a continuous monitor on the recorder 54*. Thus,two records are made of the picture, one corresponding to alternatepositively modulated complete cycles (recorder 54 and the othercorresponding to the intervening negatively modulated complete cycles(recorder both of which recorders are applied with A. V. C. signalsderived from the same frequency as the picture signals and the picturesignals themselves being used for that purpose.

When a single record is to be made corresponding to all the completecycles, then an arrangement as schematically shown in Fig. 7 may beemployed. The amplifiers 54 and 55 may be sim ilar to the correspondingamplifiers of Fig. 6, and arranged to be fed by corresponding controlssuch as the elements H, i2, 43, M, 50, 5!, 52, 53 of Fig. 6. The outputof amplifier 54 corresponding to the positively modulated completecycles (full line curve of Fig. 1 for example) is applied to atransformer 57. The output of amplifier 55 corresponding to thenegatively modulated complete cycles (dotted line curve of Fig. 1 forexample) is passed through a modulation inverter 55 of any well-knowntype whereby the negative modulations are inverted into corresponding'positive modulations. These inverted modulations are applied to thetransformer 51. Consequently, the picture recording apparatus 58 is fedwith 1800 cycle signals, all the cycles of which are positivelymodulated for a given shade value of the transmitted picture.

Wherever in the foregoing specification and in the claims, reference ismade to a modulation of a carrier wave in the same direction it is notintended to be limited to a uni-directional wave. In the same directiontherefore, refers to the amplitude or envelope area of the modulatedwave as compared with the amplitude or envelope area of the unmodulatedwave. The main object so far as gain control is concerned, is that formessage signals of the same signal strength, the average amplitude orthe average envelope area of the transmitted wave is approximately thesame where the wave is modulated or demodulated. In its broader phaseshowever, it is not necessary that the positive and negative modulationsbe of equal amounts so long as for a given signal strength the ratios ofthe positive and negative modulations bear a predetermined ratio.Likewise, while amplitude of the carrier wave is referred to, it isintended to refer either to the average amplitude over a half cycle orto the area of the envelope of the carrier corresponding to a signalmodulation.

What I claim is:

l. The method of signaling which includes the steps of generating asignaling wave of uniform frequency, modulating alternate completecycles in one direction in accordance with signals of a certaincharacter, and modulating the intervening complete cycles in theopposite direction in accordance with signals of the same character asthe first-mentioned signals.

2. The method of signaling which includes the steps of generating a waveof uniform frequency, modulating each complete cycle of said wave bysignals, cyclically varying the amplitude of said modulated waves byother waves of the same frequency but with alternate complete cycles ofsaid other waves out of phase with the first waves whereby the resultantwave has alternate complete cycles modulated positively and interveningcomplete cycles modulated positively but with both cycles representingthe same character of signal.

3. The method of signaling which includes the steps of generating at auniform frequency spaced groups of waves and at the same frequency otherspaced groups of Waves, cyclically varying the amplitude of said otherwaves in one direction by signals, and cyclically varying the amplitudeof the other waves in the opposite direction, both sets of variedamplitude waves representing the same character of signal.

4. The method according to claim 3 in which cyclical variation of saidwaves is effected at the modulating alternate complete cyclesproportionately to signals while maintaining the intervening completecycles of uniform amplitude.

7. The method of transmitting a signal of a certain character whichincludes the steps of generating a wave of uniform frequency, increasingthe amplitude of alternate complete cycles under control of said signal,and decreasing the amplitude of the intervening complete cycles by saidsignal, whereby successive complete'cycles represent the same characterof signal.

8. The method of transmitting a signal over a transmission link which issubject to fading which includes the step of translating the signal intoa uniform frequency wave of at least two complete cycles of uniformfrequency, one cycle being modulated positively proportionate to thesignal and the other complete cycle being modulated negativelyproportionate to the same signal.

9. The method of signaling which includes the step of generating a waveof uniform frequency wherein alternate complete cycles are modulated inone direction for one signal strength and the intervening completecycles are modulated in the opposite direction for the same signalstrength whereby the average of the wave amplitudes remainssubstantially constant for said one signal strength.

10. A signaling system including means for generating Waves of uniformfrequency, means to produce a signal of a given character, and means tomodulate alternate complete cycles of said uniform frequency waves inone direction by said signal and the intervening complete cycles intheopposite direction by the same character of signal wher by the averageamplitude of the modulated carrier over said alternate complete cyclesis substantially uniform.

11. A signaling system having means to generate a wave of uniformfrequency, and means to modulate said wave so that alternate complete'cycles are modulated positively and intervening complete cycles aremodulated negatively, whereby the average amplitude of the modulatedwave over complete cycles representing the same signal carrier issubstantially uniform.

12. A signaling system having means to generate a wave of uniformfrequency, and means to modulate said wave so that alternate completecycles are modulated in opposite directions and the average value of theWave for a uniform signal strength remains substantially constant.

13. A signaling system having means to gen erate message signals, anetwork upon which said signals are impressed, said network includingmeans to convert the signals into a uniform frequency wave with certaincycles modulated in one direction according to a given signal strengthand other cycles modulated inthe opposite direction according to thesame signal strength.

14. A signaling system according to claim 13 in which said network is inthe form of a Wheatstone bridge having means to impress across onediagonal of the bridge, a uniform frequency wave having the modulationphase reversed at regularly recurrent intervals.

15. A signaling system according to claim 13 in which said convertingmeans includes a modulator, means to impress'on said modulator carrierwaves, and means to impress on said modulator other waves of the samefrequency as said carrier waves but with alternate cycles reversed inphase with respect to the carrier cycles.

16. A signaling'system comprising a source of message signals, amodulator network, means to control said network by said signals, meansto control, said network by a carrier frequency wave, said signalsnormally coacting with said carrier frequency .to produce in the outputof the modulator a carrier wave having the amplitude modulated in thesame direction for a given message signal, and means to impress uponsaid modulator another wave and the same frequency of said carrier buthaving alternate cycles 180 out of phase with the carrier wave wherebythe output of said modulator consists of a modulated wave of saidfrequency wherein the average wave amplitude for a given signal isapproximately the same as the unmcdulated carrier wave.

17. A system according to claim 16, in which the means to impress saidother waves on the modulator network includes a constantly operatingreversing switch.

18. A signaling system comprising a source of message currents,'amodulator network, means to impress upon said network carrier frequencywaves, said message currents normally coacting with said carrier wavesin said network to produce a carrier having its amplitude modulated inone sense corresponding to like message signals, and means to cause saidsignals to modulate the wave so that for like signals, the averageamplitude of the modulated wave is approximately the same as theamplitude of the unmodulated wave, the last-mentioned means includingmeans to impress upon said modulator two sets of waves of said carrierfrequency, one set being continuously in phase with said carrierfrequency and the other set being 180 out of phase with said carrierfrequency.

19. In a signaling system, a source of message signals, a modulatornetwork having an input branch and an output branch, means to controlthe input branch by said signals and by a source of carrier frequency,and means to control the output branch by current of said carrierfrequency but with alternate complete cycles 180 out of phase with thecorresponding alternate complete cycles of said carrier frequency.

20. A system according to claim 19, in which the last-mentioned meansincludes a transformer having a pair of primary windings and a secondarywinding and means to energize said primary windings at said carrierfrequency but at 180 out of phase with each other.

21. A system according to claim 19, in which the last-mentioned meansincludes a pair of transformers, each having a pair of primaries and asecondary, means to energize a primary of each transformer in phasesynchronism at said carrier frequency and means to energize the otherprimary winding of each transformer at said carrier frequency but at 180phase displacement.

22. A system according to claim 19, in which the last-mentioned meansincludes a rotary inductor having a pair of pick-up windings energizedthereby, the energization being displaced by 180.

23. In a signaling system, a source of message signals, a modulatornetwork, a rotary inductor, a pair of pick-up coils for said inductor,means to rotate said rotor so that one coil is energized in spacedcomplete cycles with the spacings of complete cycle length, the othercoil being energized in spaced complete cycles during the spacings whenthe first coil is deenergized, means to control said network by saidmessage signals, means to control said network by the current from saidpick-up coils whereby the output of said modulator network for a givensignal strength consists of a modulated current of uniform frequency butwith the average Wave amplitude approximately the same as the amplitudewhen no 'signals are being impressed on said network.

24. In a signaling system, a source of message signals, a modulatornetwork, a grid-controlled amplifier having its input fed from saidinput, means to control said modulator by said message signals and by acarrier frequency and means to vary the bias on 'said tube at saidfrequency so that alternate complete cycles are out of phase with thecycles impressed thereon from said modulator network, whereby successivecycles representing the same signal character are modulated in oppositedirections.

25. A system according to claim 24 in which the last-mentioned meansincludes a transformer having a pair of primaries and a secondary, saidprimaries being energized in spaced complete cycles at said carrierfrequency with the energizations alternating and said secondary beingconnected to the input circuit of said tube.

26. A signaling system including means for generating waves of uniformfrequency, means to modulate said waves by a signal of a given characterso that succeeding cycles are modulated in opposite directions wherebysaid average amplitude of the modulated wave representing said signalremains substantially uniform, and receiving apparatus including meansto reproduce said signals and means to control the gain in the receivingapparatus under control of the received signals.

27. A signaling system having means to generate a wave of uniformfrequency, means to modulate said wave so that for a given signal,succeeding cycles are modulated in opposite directions whereby theaverage amplitude of the modulated wave representing said signal remainssubstantially uniform, a receiver having means to reproduce the signalsunder control of the received waves, and means to control the gain inthe receiver, the average amplitude of the received wave for said givensignal closely approximating the average amplitude of the received wavewhen unmodulated.

28. A signaling system having means to generate a carrier of uniformfrequency, means to modulate said carrier by a signal of a givencharacter so that the average amplitude of the modulated carrier closelyapproximates the amplitude without modulation, a receiver forreproducing said signals, means to utilize certain cycles of themodulated waves for signal reproduction, and means to utilize othercycles for controlling the gain in the receiver.

29. A system according to claim 28, in which the last-mentioned meansincludes a distributor for diverting the signal reproducing cycles intoone channel and the gain control-cycles into another channel.

30. A signaling system having means to gen* erate a wave of uniformfrequency, means to modulate said wave so that for a signal of a givencharacter certain cycles are positively modulated and other cycles arenegatively modulated whereby the average amplitude of the modulated waverepresenting said signal remains substantially uniform, a receiver and adistributor associated with said receiver for diverting the positivelymodulated waves into one channel and the negatively modulated waves intoanother channel.

31. A system according to claim 30, in which one of said channels is asignal reproducing channel and the other is a gain control channel.

32. A system according to claim 30, in which each of said channels isprovided with a separate signal reproducer.

33. A signaling system according to claim 30, in which one of saidchannels is provided with a reproducer for producing a positive visualrecord of the signals and the other channel is provided with areproducer for producing negative visual records of the signals.

34. A signaling system having means to generate a Wave of uniformfrequency, means to modulate said waves for signals of a givencharacter, so that certain cycles are positively modulated and othercycles are negatively modulated, a receiver, a distributor associatedwith said receiver for diverting the positively modulated waves into onechannel and the negatively modulated waves into another channel, meansin said other channel to invert the modulation envelope of the wavestherein, the output of both said channels being applied to said receiverto reproduce the signals.

35. A system according to claim 34:, in which each of said channels isprovided with gain control means which is controlled by the amplitude ofthe received waves.

36. The method of signaling which comprises generating a uniformfrequency wave with certain cycles positively modulated by a signal of agiven character and other cycles negatively modulated by the same signalcharacter, receiving the positive and negative modulated wave, divertingthe positive modulated wave into one channel, diverting the negativemodulate wave into another channel, and reproducing the signal undercontrol of the output of said channel, one of said channels being usedas gain control for the other channel.

37. The method of signal transmission employing a uniform frequency wavewhich includes the steps of modulating said wave so that for signals ofthe same character, the average amplitude of the wave is approximatelythe same as the average amplitude of the unmodulated wave, receivingsaid modulated wave, applying alternate complete cycles to control areproducer and applying alternate intervening cycles to control the gainin said reproducer.

AUSTIN G. COOLEY.

